1. Field of the Invention
The present invention relates to a shrinkable polyamide film and a process for its producition, and particularly to a shrinkable polyamide film having good gas impermeability and a process for its production.
A object of the present invention is to provide a shrinkable polyamide film for wrapping, which is highly shrinkable and strong and has a shrinkage stress within a range of from 300 to 700 g/mm.sup.2 which is suitable for various applications. A secondary object of the present invention is to provide a shrinkable polyamide film which has high gas impermeability as well as the above properties.
2. Description of the Prior Art
As shrinkable plastic films, films composed of copolymers of polyvinyl chloride, polyvinylidene chloride, polylefins, etc. are available, and they are used for wrapping hams, sausages and various other articles. However, these films have certain drawbacks, for instance, such that they lack strength and are susceptible to rupture or formation of pin holes, or they lack oxygen impermeability and tend to permit the penetration of oxygen through the wrapping films, thus leading to degradation of the quality of the wrapped articles.
As shrinkable polyamide films, films composed mainly of a 6-nylon homopolymer or a copolymer of m-xylylenediamine with an aliphatic carboxylic acid, are available, and they are superior in their strength. However, the former have high crystallinity and accordingly a low hydrothermal shrinking ratio, and they are likely not to well fit on the wrapped contents. Whereas, the latter have a high Young's modulus and a high hydrothermal shrinkage stress, and they tend to lead to a deformation of the wrapped contents or rupture of sealing portions. Further, these films likewise lack oxygen impermeability and tend to lead to degradation of the quality of the wrapped contents due to the penetration of oxygen through the films.
Because of these drawbacks, they are not fully satisfactory for the intended purpose although they have a superior property, i.e., high strength.
There is no shrinkable film presently available which has good gas impermeability. Thus, there is a strong demand in the wrapped food industry for the development of shrinkable films having good gas impermeability.